1. Field of Invention
This invention relates to wastewater and solid treatment, specifically the extraction of biofuels from Grease and Biosolids.
We have invented a novel method to stabilize triglycerides in FOG (Fats, Oil and Grease) commonly referred to as trap grease. This stabilization is achieved inside the grease interceptor or grease trap, therefore representing an in-situ process. Stabilization is achieved by arresting hydrolysis thus preventing the BTU-rich triglycerides breaking down into free fatty acids (FFA). Applicant's invention treats (stabilizes) the FOG content considered solid waste and not the wastewater content. This distinction is important as other methods know in the art treat the wastewater to achieve required discharge parameters but do not address the treatment (stabilization) of solid waste to produce a usable product such as fuel. A low FFA concentration as well as sulfur reduction is highly desirable, allowing for easy biodiesel fuel conversion or biogasification. Although this invention is perfectly capable of being used as a stand-alone embodiment, it was tested non-commercially over the last year together with a device for in-situ bioremediation of liquid waste (U.S. Pat. No. 7,615,156 granted on Oct. 10, 2009) to establish a reduction to practical application. The details of the system have neither been published, shown to the public nor sold as of this filling.
2. Background of the Invention
Construction and performance of Grease Interceptors (GI) and Grease Traps (GT) are regulated by ASME and ANSI standards A112 14.6 2010 and Z1001. The difference between a GI and GT is defined by ANSI as follows: While a GI and a GT are similar in function, they are distinguished by their size and location of install. GT's are smaller and range from 10 to 500 gallon in capacity and are usually installed in the kitchen under the sink. GI's are larger structures installed under ground and a size larger than 500 gallons. It is a requirement of the A112 14.6 standard to not introduce any device into a GI or GT that alters the “flow and separation characteristics” of the GI/GT. This requires any treatment of the contained FOG to not alter the critical base functions of a GI/GT.
The National Renewable Energy Laboratory (NREL), among other reputable information sources, published technical assertions on the method and viability of extracting fuel (biodiesel) from trap grease, also known as FOG or brown-grease. While yellow-grease (used fryer oil etc.) is comparatively easy to recycle due to its low free fatty acid content (4% to 15%), commercial fuel extraction of brown-grease has been most difficult due to the chemical makeup of the trap grease and its sulfur content. A method to pretreat brown-grease to overcome those difficulties would be most desirable. According to the NREL study titled “Urban Waste Grease Resource Assessment”, each US resident produces 13.37 pounds of brown-grease per year resulting in 4-billion pounds of brown-grease produced annually. Given the proper methodology as well as technology an estimated 945-million gallons of biodiesel could be created annually.
NREL states that the Free Fatty Acid (FFA) content in brown-grease ranges from 50% to 100%. This high FFA concentration is generated when triglycerides break down to their individual molecular strands, known as monoglycerides, through a process known as hydrolysis. Triglycerides contain much more BTU per weight than FFAs. The technical and capital requirements to turn FFAs into biodiesel or to separate FFAs and triglycerides are enormous and represent, so far, an insurmountable barrier to widespread commercialization. The conversion of triglycerides to biodiesel is much simpler and is achieved by a process called transesterification. However, FFA contents above 4% create a loss of clean oil yield that increases with FFA concentration. A 10% FFA concentration can result in a 30%-plus yield loss. Transesterification can typically handle only <4% FFA content and requires a process called caustic stripping. Four percent to 20% FFA concentration uses a 2-step process called acid esterification and subsequent base esterification. This method is expensive, complex and energy intensive. Brown-grease, when delivered to a processing plant, contains 50% to 100% FFAs, and as of this writing technologies that can achieve partial biodiesel conversion currently exist only in small pilot plant form. According to the NREL there is no proven technology above 50% FFA mixes. As it becomes evident a modification of the brown-grease FFA content is desirable. When grease in the form of FOG is discharged from FSEs (Food Service Establishments) into a GI/GT the FFA content is well below 4%. FFAs form with the hydrolysis that occurs inside a GI/GT. Said hydrolysis is enabled by the anaerobic conditions inherent inside a GI/GT. Anaerobic and chemical microbial activities cause the breakdown of the triglycerides into FFAs whilst releasing hydrogen sulfide, which in turn acidifies the GI/GT content thus accelerating hydrolysis and the destruction of the BTU rich triglycerides. However, hydrolysis will not occur if the GI/GT is kept in a continuous aerobic state. Thus an aeration method sufficient enough to evenly distribute and recirculate the entire GI/GT content of both water and FOG to maintain a dissolved oxygen level of >0.5 mg/l will arrest virtually all hydrolytic reactions in said GI/GT. It is important to point out that said dissolved oxygen level of >0.5 mg/l must also be achieved in the FOG content to prevent hydrolysis. However, due to the above mentioned ANSI requirements the aeration method and technology must be capable of dissolving enough oxygen while not interfering with the inherent functions of a GI/GT. One such method is one of the applicants' earlier inventions U.S. Pat. No. 7,615,156 “device for in-situ bioremediation of liquid waste”. This technology has also been certified to be compliant with the above-mentioned ANSI Standard. For the purpose of explaining our methodology applicants will refer to the above-mentioned patented device as means for aeration and biological treatment. However, this should not be construed as a limitation, as any aeration device suitable whilst still fulfilling the Standards requirement, can be used.